As the demand for hydrocarbon-based fuels has increased, the need for improved processes for separating hydrocarbon feedstocks of heavier molecular weight has increased as well as the need for increasing the conversion of the heavy portions of these feedstocks into more valuable, lighter fuel products. These heavier, “challenged” feedstocks include, but are not limited to, low API gravity, high viscosity crudes from such areas of the world as the Middle East, Mexico, Venezuela, and Russia, as well as less conventional refinery feedstocks derived from such sources as bitumen, shale oil and tar sands. It is also important that heavy crude fractions, such as atmospheric resids, vacuum resids, and other similar intermediate feedstreams containing boiling point materials above about 850° F. are processed in such a manner so as to improve their ability to be utilized as feedstreams for subsequent refining and petrochemical processes such as, but not limited to, fuels blending, fuels upgrading, catalytic conversion, steam cracking, and lube oils production and upgrading.
Most crude oils and synthetic crude oils derived from such raw materials as bitumen, shale oil and tar sands are processed through initial separations units such as a crude unit that are designed to boil and distill lighter boiling point fractions from the heavier boiling point crude fractions. The majority of these boiling point fractions are sent to other refinery and petrochemical processes for further refinement depending upon their molecular content characteristics, while a smaller amount of these crude unit fractions are sent to finished product treatment and/or product blending.
One problem that exists is that these conventional separations units require a significant amount of energy to generate these distillation based separations. Most crude units have at least one atmospheric distillation train and at least one vacuum distillation train. Often crude units also have additional crude intermediate or auxiliary distillation trains. Each of these unit trains require the hydrocarbon feed to the train to be heated to temperatures of about 750° F. to about 850° F. prior to entering a distillation column associated with each train. In turn, each of these distillation columns normally requires multiple reflux circuits and possible intermediate column reheat circuits in order to properly control and achieve proper separation of the individual fractions obtained from the distillation. Not only does this arrangement require a significant amount of equipment and associated capital and maintenance costs, but these conventional processes require large amounts of input energy as well as a large array of sophisticated controls and skilled personnel for proper operation.
Another problem that exists in the art with heavy oils separations is that these crude distillation processes only separate the molecules of the feedstreams by boiling point. Therefore, molecules with close boiling points are removed together in a single fraction from the crude distillation processes. In particular saturated and aromatic hydrocarbons with the same or close carbon content (for example hexane and benzene which both have 6 carbon atoms) cannot be easily separated by commercial crude distillation processes and both molecules remain in a single stream of the crude unit fractions. Additionally, these types of molecules are very difficult to separate in subsequent refinery and petrochemical processes especially in distillation based processes. Most of the subsequent separations processes either rely on solution extraction processes or on other characteristics of the molecules such as their freeze points in order to separate these different close boiling point compounds. Therefore, as these ancillary processes tend to be expensive and very “targeted” as to the separations being achieved, typical refinery and petrochemical aromatics/saturates separations processes are generally limited to processes wherein a specific, small boiling point range of compounds are involved in the separation and/or wherein the separations must be made to within a high degree of purity.
Therefore, there exists in the industry a need for improved low energy refinery and petrochemical processes that can achieve a separation of hydrocarbon components by molecular species, in lieu of separations by molecular weight or boiling points. Even greater is the need for a relatively simple, low energy saturated hydrocarbons separations process that can make a bulk separation of high saturates content product streams from a heavy hydrocarbon feedstream, preferably a crude oil or crude resid hydrocarbon stream, without the use of conventional technologies for the separation of targeted molecular species such as extractive solvent processes.